With the remarkable development of small, thin, and high-functionality portable electronic devices, there is a growing demand for smaller, thinner, and high-capacity batteries and battery packs as the power source for these devices. Lithium batteries are known to be easily made small and to have high capacity. In particular, flat prismatic lithium ion rechargeable batteries that can be repeatedly used are suitable for the devices to be made thinner, and therefore they have been increasingly used as the rechargeable battery for portable electronic devices such as mobile phones.
Since lithium batteries have high energy density and contain a flammable organic solvent as liquid electrolyte, it is essential to take account of safety features, i.e., they need to incorporate such features as to ensure that no damage is caused to the device or injury to the user, even if the battery should fall into an abnormal condition. For example, if the battery positive and negative electrodes are short-circuited for whatever reason, a large short-circuit current flows in high energy density batteries, whereupon the inner resistance generates Joule heat and the battery temperature rises. A temperature rise in the battery leads to rapidly built-up gas pressure resulting from chemical reactions between positive electrode active materials and electrolyte, or from evaporation or decomposition of electrolyte, which may cause fire or explosion of the battery. Batteries may fall into a high-temperature state not only because of external short-circuiting but also of rechargeable battery overcharge. The same applies if the portable electronic device installed with the battery is placed near a heater, or left inside a car parked in a hot weather environment.
Lithium batteries are normally provided with safety features for preventing batteries from falling into an abnormal state and for evading a further dangerous state should the battery fall into an abnormal state. Such features may be incorporated in the battery as its own nature, e.g., active materials of the electrode plates and electrolyte may be made not to be excessively reactive, or, a polyolefin porous film may be employed for the separator because it has a “shutdown function”, as the minute pores melt and close under an abnormally high temperature. A thermal fuse which shuts the I/O circuit upon an abnormal temperature rise, or a safety vent for letting out built-up internal pressure may also be provided. Cylindrical lithium batteries may further be provided with a protection feature such as a Positive Temperature Coefficient (PTC) element connected in series to the I/O circuit at the sealing end, which restricts overcurrent caused by external short-circuiting.
Smaller batteries and prismatic batteries cannot be provided with the thermal fuse or PTC element inside the battery, and therefore these components are normally disposed outside the battery and electrically connected to the battery. In the case of rechargeable batteries, they are further provided with a circuit substrate including a circuit for protecting the battery from overcharge and overdischarge, and these constituents outside the battery are all accommodated in a pack case together with the rechargeable battery to form a battery pack.
Pack cases are usually manufactured by resin molding technology, and the fabrication cost of molding dies for the resin molding tends to be high, because of which pack cases generally cause high costs. Moreover, the time required for designing the molding dies is relatively long, which makes difficult the application of battery packs to portable electronic devices such as mobile phones, which are re-modeled in short cycles. Another problem is that battery packs allow themselves to be made smaller and thinner only to a limited extent because of the limitation on the thickness moldable in resin molding and because of the need to retain certain strength of the battery pack.
In order to prevent the danger of disassembling batteries and battery packs for wrong use or for satisfying curiosity, batteries and battery packs also need to have such a design as to be hardly disassemblable or a design which alerts the user that the batteries have been disassembled. Also, taking account that they are used for portable electronic devices, batteries and battery packs are required to have a rigid structure which can withstand vibration or shocks in a falling accident, as well as a water-proof structure particularly for the electronic circuit portion. In response to these demands, there have been proposals to unite a circuit substrate including battery protection circuits and a battery by resin molding, so as to realize a hardly disassemblable, rigid, water-proof structure.
The applicants of the present invention have so far proposed a resin mold battery pack in Japanese Patent Application Nos. 2000-320166 and 2000-363518, in which a rechargeable battery and a circuit substrate are fixedly connected by a connection member and placed inside a molding die as an intermediate product, and resin is filled around the intermediate product such as to expose external terminals on the circuit substrate to the outside, to unite the rechargeable battery and the circuit substrate.
Japanese Patent Laid-Open Publication No. 2000-315483 discloses a structure wherein a rechargeable battery and a circuit substrate connected by a connection member are placed inside a molding die, and the substrate is resin-packed and fixed on the battery or its lid case, or both the substrate and the battery are resin-packed.
To mount electronic components such as the above-mentioned thermal fuse or PTC element on small batteries used as a power source for portable electronic devices, these need to be accommodated with the battery in a case in the form of a battery pack, which tends to cause high costs. On the other hand, it is important that these thermo-sensitive elements (thermal fuse and PTC elements) are disposed in heat-coupled arrangement with the battery, i.e., they need to be united with the battery. Thus, there is a demand for a one-piece structure which is not like a conventional battery pack but allows a thermo-sensitive element outside the battery to be united with the battery.
In rechargeable batteries, battery temperature is detected for controlling charge level and other safety features. Therefore, rechargeable batteries include a temperature detection sensor such as a thermistor contacted thereto which inputs detected information to the control circuit. Their external terminals are exposed to contact terminals on the charger side. In order to provide such a temperature detection sensor, the rechargeable battery needs to be designed as a battery pack, which requires a larger number of steps in its manufacture process and tends to cause high costs because of the need to provide a structure to ensure precise detection of battery temperature.
Positive and negative electrodes of small batteries are formed on different surfaces because of their size restriction. If they were formed on the same plane or on any arbitrary surface easy for connection, they would be much more conveniently used. For example, since cylindrical batteries normally have their positive and negative electrodes on the opposite ends, the device in which the batteries are used requires to have connection members for both electrodes on both sides of the battery accommodating space. Prismatic batteries have their positive and negative electrodes on the sealing end, but they are formed on different, stepped surfaces, causing the external connection structure to be complex. Thus, there is a demand for a simpler external connection structure for positive and negative electrodes of batteries in accordance with the trend of smaller and thinner devices.
When uniting a battery and a circuit substrate by resin molding, there was a problem that resin does not form good enough a form with the battery or substrate, and so it was necessary to encapsulate the battery and substrate by a resin mold package, resulting in a structure very similar to a battery pack in which a battery and a substrate are accommodated in a resin mold pack case. This was contrary to the demand for smaller and thinner batteries.
In the structure disclosed in the above-mentioned Japanese Patent Laid-Open Publication No. 2000-315483, the circuit substrate is first fixed to the battery by a double-sided adhesive tape before resin molding is performed such that resin covers at least three faces of the battery. While the battery and substrate are fixed to each other, resin itself is not bonded to the metal surfaces. Therefore, there is the risk that resin mold package may peel off from the battery if subjected to vibration or shocks. If the batteries and battery packs are designed mainly for portable electronic devices, resin mold package should be engaged firmly with metal surfaces of the battery, since vibration and shocks are inevitable.
In the above-mentioned prior art, the battery pack has an external connection structure in which connectors are provided at the tips of the leads drawn out from the resin-packed circuit substrate to the outside for male-female connection coupling with the device side. This will present no problem if the device is large and offers enough space for accommodating the battery. The battery packs to which the present invention is directed are primarily designed for small devices where battery accommodation space is scarce, and therefore cannot adopt such external connecting structure. Instead, the battery and battery pack of the present invention need to have a connection structure in which, when the battery or battery pack is inserted in the space provided on the device side, the connection terminals or probes on the device come into pressure contact with external terminals exposed to the outside in a predetermined position of the battery or battery pack. If the battery pack is constructed to contain a battery and a circuit substrate formed with external terminals and if these terminals are to be brought into pressure contact with the connection terminals on the device side in the battery accommodating space with low contact resistance, the battery pack must have very accurate outer dimensions and its external terminals must be located precisely. If the dimensional precision is low, the contact resistance between the device-side connection terminals and external terminals will become high, leading to malfunctions such as contact failure and voltage drop.
An object of the present invention is to provide a battery united with a substrate by resin molding and a battery pack of a battery and a substrate united by resin molding.